Tire Replacement Guidelines

When to replace bicycle tires? Many websites state "3 years" or "3,000 km," but it's often unclear if your bicycle's tires actually need replacing.

For example, if you commute or go to school 5 km one way, that's 10 km round trip per day.

If you commute or go to school about 250 days a year, but don't ride on rainy days, you might ride about 150 days a year.

10 km × 150 days = 1,500 km

This means you would reach 3,000 km in about two years.

And here's a lesser-known fact: the biggest factor in tire degradation isn't wear and tear.

The number one enemy is "UV light."

As a mechanical designer, I know that plastic and rubber parts on outdoor machinery degrade severely. I always struggle with countermeasures, so I'm well aware of this from experience.

UV light chemically degrades rubber.

It makes them more prone to cracking and wear, causing adverse effects.

You can mitigate this degradation by parking your bike in a shaded area or using a UV-cut bicycle cover.

■ Things to check when replacing

It's difficult to determine the exact time to replace tires.

While obviously degraded items are out of the question, making a judgment call at the borderline can be tricky.

This time, I have an actual example that falls into a subtle area, so I'll show you with images.

Upon inspection, I found a crack in the rim area.

There's a crack and a bit of rust visible.

By the way, this is the front wheel.

The rear tire didn't seem to have any cracks.

When replacing, it might be necessary to address not just the tire but also the sidewall.

There's a crack in the tire itself.

You need to assess how deep the crack is.

As you can probably see in the image, woven wires are visible through the crack.

This is the casing, which forms the shape of the tire.

Normally, the casing becomes visible due to wear, but here, the crack has suddenly reached the casing.

It would be better to replace this.

I've suddenly concluded that it's "better to replace," but I'd also like to check the tread of both the front and rear tires.

This is the condition of the rear tire.

Although it's somewhat worn, the tread is still visibly present, so replacement might be okay a little later.

This is the condition of the front tire.

There isn't much tire wear, so it seems fine to continue using it as is.

Comparing the front and rear tires, for me, the rear tire seems to wear out faster.

■ Choosing tires

So, the front tire had a crack on the sidewall, and the rear tire had some wear.

The front tire definitely needs replacing, and the rear tire is a difficult call.

However, since the front tire is being replaced, I decided it would be better to replace the rear tire as well.

Now, once you've decided to replace both front and rear tires, first find out your tire size.

The tire size is written on the sidewall of the tire.

You won't find it by looking at the bicycle itself.

Looking at the text written on the tire sidewall, it said:

"MAXIMUM RECOMMENDED INFLATION PRESSURE 110 P.S.I 7.7BAR770KPA"

It looks like a spell.

For me, not being from an English-speaking country, I didn't get any information from it.

The "MAXIMUM RECOMMENDED INFLATION PRESSURE" part would probably mean "Maximum Recommended Air Pressure."

Once I understood it, it wasn't that difficult.

Since it seemed to be about air pressure, it wasn't the tire size.

But since we're here, let's decode the next enigma as well.

The next "110 P.S.I 7.7BAR770KPA" actually contains three pieces of information written consecutively.

Broken down, it's:

"110 P.S.I", "7.7BAR", and "770KPA".

"P.S.I" stands for pounds per square inch, written in the imperial system.

By the way, countries that use this unit seem to be only the US, Myanmar, and Liberia.

Even so, it comes first, so America is strong.

Next, "BAR" is bar.

It was a unit once used in Japan as well.

Even in weather forecasts, "millibar" was used.

Recently, it's "hectopascal," isn't it?

The relationship between PSI and BAR is "100 PSI = 6.89 BAR."

So, 110 PSI = 7.58 BAR, which is rounded to 7.6 BAR.

There's a slight error, but 110 PSI = 7.7 BAR is written on the tire surface.

And "KPA" stands for kilopascal.

Since "1 BAR = 100 kilopascals," 7.7 BAR = 770 KPA.

In simple terms, three units are written.

They all refer to the same pressure.

And since converting them is difficult, the converted values are listed for each.

To digress, the tire size was noted elsewhere.

It says "25-622" and "700×25C".

"25-622" written before "700×25C" is the ETRTO standard, which specifies the rim width and bead width.

The latter part, "700×25C," indicates the tire size: 700 mm (70 cm) diameter × 25 mm (2.5 cm) width.

Searching on Amazon with the keyword "700×25C" yielded 48 products, ranging from about 2,500 yen to 26,000 yen.

Since both need to match, searching for "25-622" and "700×25C" is the correct way.

Also, there are three types of tire shapes, so check that as well.

By the way, these shapes are "tubular tires," "clincher tires," and "tubeless tires."

You'll need to choose by considering the features and your budget.

There are also colored tires, such as "white" or "red," in addition to "black," and puncture-proof (punctureless) options.

You'll choose what you like and what your wallet allows.

Do you now have an idea of when to replace your tires and which ones to choose?

Please check your tires!